Wee asked me to post this.

I have come to the conclusion that the new skill, is in fact, SLAVERY.

It fits almost all of the criterion.*It can extend the map, we'd need new lands to explore and find indigenous tribes to enslave.*It could be a whole new game in itself.*It's never been done before.*It would use a whole new game mechanic. Using enslaved people to train for you.*It would introduce a whole new type of gameplay.*It is unique, and it could involve combat, like trapping the tribes without them killing you with spears and such.*It will involve all the skills, because your slaves will train for you.*Training will not be money driven or cost a lot. (Because you don't have to pay them)*A ship is featuring in it quite prominently. (Gotta transport them somehow.)